What is the critical angle of attack?

What is the critical angle of attack?

• A. The angle of zero lift
• B. The angle at which a wing stalls
• C. The angle of maximum lift
• D. The angle at which drag is minimized

Answer: (B)

The critical angle of attack is the angle of attack at which the airflow over the wing can no longer remain attached, causing the boundary layer to separate and the wing to stall. As the wing tilts to higher angles, lift increases up to this point, but beyond it the flow detaches from the surface, dramatically reducing lift and increasing drag. This stall onset angle depends on the airfoil shape and flight conditions, so it’s the specific angle where lift no longer continues to rise with angle and stall occurs. It’s not the zero-lift angle, which is where lift becomes zero, nor the angle of maximum lift (that occurs just before stall and is slightly lower than the critical angle). It’s also not the angle where drag is minimized, since the lowest drag-to-lift ratio happens at a different point along the lift-drag curve. In short, the critical angle of attack marks the onset of stall.

The critical angle of attack is the angle of attack at which the airflow over the wing can no longer remain attached, causing the boundary layer to separate and the wing to stall. As the wing tilts to higher angles, lift increases up to this point, but beyond it the flow detaches from the surface, dramatically reducing lift and increasing drag. This stall onset angle depends on the airfoil shape and flight conditions, so it’s the specific angle where lift no longer continues to rise with angle and stall occurs. It’s not the zero-lift angle, which is where lift becomes zero, nor the angle of maximum lift (that occurs just before stall and is slightly lower than the critical angle). It’s also not the angle where drag is minimized, since the lowest drag-to-lift ratio happens at a different point along the lift-drag curve. In short, the critical angle of attack marks the onset of stall.